It is sometimes desirable to increase the modulus of rubber compounds. For instance, it is generally desirable to increase the modulus of rubber compounds which are utilized in tire tread base compositions and in tire wire coat compounds. A higher degree of stiffness in such rubber compositions is conventionally attained by incorporating larger amounts of fillers, such as carbon black, into the rubber compounds and/or by increasing the state of cure of such compounds. Unfortunately, both of these techniques generally lead to undesirable results. For instance, the incorporation of additional carbon black into rubber compounds typically leads to high levels of hysteresis. Accordingly, the utilization of such compounds in tires results in excessive heat buildup and poor cut growth characteristics. The utilization of high amounts of sulfur to attain a high state of cure typically leads to poor aging resistance. Furthermore, it is highly impractical to reach high levels of stiffness by increased state of cure alone. For these reasons, it is not usually possible to attain the desired degree of stiffness in tire tread base compounds by simply adding higher levels of fillers or curatives.
It is also known that the modulus of rubbers can be increased by blending various rigid polymers therein. For instance, polyesters can be blended into rubbers to increase the modulus of the rubber. However, such rubber/polyester blends typically display elongations which are greatly reduced. In other words, such standard blending techniques can be utilized to increase the modulus of rubbers but such techniques are very detrimental with respect to elongation.